Construction Of Ni_xP_y/g-C₃N₄ Complex Materials And Research On Photocatalytic Hydrogen Production From Water Splitting

The circumstance of energy shortage seriously restricts the progress of the society.Clean and renewable hydrogen?H₂?has the advantages of high combustion calorific value,environmental protection and simple way of storage,considered as the most promising new energy in the 21st century.Photocatalytic water-splitting technology is very conducive to the preparation of hydrogen energy,whose key is the development of high-performance and durable photocatalytic materials.Also,photocatalytic material is the key of achieving the efficient conversion of solar energy to hydrogen energy.Graphite-phase carbon nitride?g-C₃N₄?is a new kind of photocatalytic organic material with excellent photocatalytic properties produced by polymerization.At present,it is a hot material for photocatalytic research prepared by vapor deposition method,solvothermal method or thermal polycondensation method.However,the performance of pure g-C₃N₄ cannot reach up to the level of practical application.In order to improve the transmission ability of photogenerated carriers and photocatalytic activity of g-C₃N₄,metal-based cocatalysts are selected to combine with nitride carbon,effectively improving the photocatalytic performance of the g-C₃N₄ material.According to the previous reports,transition metal phosphatides are usually used to study photocatalysis or electrocatalysis,which can improve the carrier separation efficiency of semiconductor photocatalytic materials,so it is an ideal choice as cocatalyst of g-C₃N₄.Therefore,this paper will determine g-C₃N₄ as the main catalyst and Ni metal phosphatide as the cocatalyst to synthesize Ni_xP_y/g-C₃N₄composite photocatalyst and the specific operation steps are as follows:?1?The ultrathin porous structure of g-C₃N₄ was obtained by calcining at high temperature,and then Ni₁₂P₅ nanoparticles were loaded on the surface of the catalyst by ultrasonic loading method.The obtained composite photocatalyst Ni₁₂P₅/g-C₃N₄had greatly high hydrogen evolution rate(632.8?mol·h^-1·g^-1)which was 89 times that of the original g-C₃N₄,showing excellent photocatalytic water splitting for hydrogen evolution activity.Moreover,the performance of composite photocatalyst was better than Pt/g-C₃N₄,making the transition metal phosphide expected to be promising substitute for precious metals.The experimental results showed that it was necessary for original g-C₃N₄ to be modified by Ni₁₂P₅ to greatly improve the light absorption capacity and carrier separation efficiency of the composite photocatalyst.This work provided effective support for the research about double modification of catalysts,taking an important step for further enhancing the activity of g-C₃N₄.?2?Ni₂P-NiP₂/g-C₃N₄ composite material,a cheap and stable catalyst,was prepared by hydrothermal method and phosphating method.When g-C₃N₄ was combined with Ni₂P-NiP₂ bi-cocatalyst,the composite photocatalyst had immensely high hydrogen evolution rate(753.8?mol·h^-1·g^-1)and tremendously enhanced light absorption capacity,which is 171 times that of the pure g-C₃N₄(4.4?mol·h^-1·g^-1)under the radiation of visible light.Meanwhile,the influence of Ni₂P-NiP₂ cocatalyst on g-C₃N₄ catalyst was analyzed and the photocatalytic mechanism of the composite catalyst exposure to visible light was explained according to various characterization tests.What's more,the photocatalytic performance of the catalyst was higher than that of two other kinds of phosphide/carbon nitride?Ni₂P/g-C₃N₄,NiP₂/g-C₃N₄?composite catalysts,indicating that the performance of bi-component Ni₂P-NiP₂ is better than that of single-component Ni₂P and NiP₂.This experiment opened a new way for the g-C₃N₄ catalyst to seek highly efficient bi-cocatalyst.?3?The g-C₃N₄ was first fabricated into ultrathin laminar structure by air stripping method,and then the Ni₂P quantum dots were loaded on g-C₃N₄ surface by electron-driving self-assembly method and phosphating method.Ni₂P/g-C₃N₄,a composite photocatalyst with 3 wt%nickel loading,had extremely high hydrogen evolution rate(1503?mol·h^-1·g^-1)and photocurrent response value?82.58?A?,which are about 120 times and 11 times that of pure g-C₃N₄ respectively,indicating that plenty of Ni₂P quantum dots have become efficient reactive sites on the surface of the catalyst.In addition,the photocatalytic activity and photoelectric activity of Ni₂P/g-C₃N₄ were about three times than that of Pt/g-C₃N₄,proving that transition metal phosphide has the potential to become an efficient and cheap substitute for precious metals as cocatalyst of g-C₃N₄.The experimental results showed that the transfer and separation efficiency of carriers were greatly improved due to the formation of stable chemical bond between Ni metal and g-C₃N₄,leading to the significant enhancement of photocatalytic activity and photoelectric activity of Ni₂P/g-C₃N₄.Additionally,g-C₃N₄/Ni₂P had the high stability based on the cyclic test,which was conducive to the actual production and application of the above bi-functional material.In order to improve photocatalytic water splitting for hydrogen evolution performance of semiconductor catalysts in visible light,this paper describes the modification of g-C₃N₄ on two aspects of morphology controlling and cocatalyst loading.The photocatalytic performance of as-prepared composite materials has been greatly promoted.Also,it is important to explore the characteristics of composite photocatalysts such as structure and physicochemical properties through a series of characterization tests,and then the catalytic mechanism is detailed explained.It is hoped that this work can provide practical and effective theoretical basis for further study of photocatalytic technology.